Figure 2: Photograph and SEM images of the four
Nutshells (NSs): AS (a, b, c); FS (d, e, f); PS (g, h, i); WS (j, k, l)
Figure 3 (a) shows the Fourier-transform infrared (FT-IR)
spectra of four NS samples confirming the presence of the functional
groups. All the NSs exhibit distinct peaks at 1033
cm−1, 2929 cm−1, and 3340
cm−1 which are attributed to the C-OH, C-H, and O-H
bonds preset in lignocellulose.[38] Distinctive
lignin peaks are found on all the NSs at 1460 cm−1,
1503 cm−1 and 1595
cm−1.[39] In addition, the
hemicellulose and cellulose are confirmed by the peaks at 1054
cm−1 which is associated to the stretching vibrations
of C─O─C.
Inside the nutshell structures, cellulose exists in the structure formed
by lignin, while hemicellulose is tangled with cellulose, filling the
gap between cellulose and lignin.[40,41] This
arrangement of these biopolymers plays a crucial role in their
structural properties. Certain chemical treatments of the nutshells
decrease the amount of lignin and disrupt the internal links among
lignin, cellulose, and hemicellulose. That results in a greater amount
of negative surface charges.[37]
The zeta (ζ) potentials were analyzed for these four NSs depicted inTable 1 . The results show a consistent range of ζ values,
between -20 mV to -35 mV for these four NSs. The BET surface areas were
analyzed before and after the acetone and ethanol solutions treatments.
The results presented in Table 1 indicates the marginal
improvement of the surface areas because of this treatment.
Table 1: BET surface area and Zeta potential
comparison of four nutshells